1. Field of the Invention
This invention relates to a metering system, and more particularly to a metering system suitable for an instrument such as a single lens reflex camera provided with a focus detecting system.
2. Description of the Prior Art
For example, there has been an idea of using a single photoelectric light-receiving means commonly for the metering and the focus detection, but generally, different characteristics are required of the light-receiving means for the metering and the focus detection. Therefore, if an attempt is made to achieve the compensation therefor on a circuit, there will occur a problem that the circuit necessarily becomes complex and the differrent characteristics cannot be sufficiently obtained. Also, particularly in a focus detecting system of the TTL image sharpness detection type, the light to be detected is the imaging light beam, but non-imaging light beam is preferable for the metering and accordingly, there occurs a fear that one of the focus detection and the metering cannot be achieved.
From such circumstances, where an attempt is made to equip a single lens reflex camera, particularly, a camera provided with a TTL type metering system, with a TTL type focus detecting system, there is adopted means of constructing these two systems in the camera entirely independent of each other, and in that case, due to the fact that the camera is a small and compact instrument, difficulties are encountered in arranging the metering light-receiving means and the focus detecting light-receiving means. Moreover, the fact that both of a metering optical system and a focus detecting optical system are required is liable to lead to inconveniences such as bulkiness of the camera and complication of the construction.